Good deal you fixed it and for free. Here's some other tips to try with misfires.
It's always a good idea to do a compression test to make sure the mechanical parts are sealing. All the tests that don't cost anything to do are the places to start.
If it misses at lower rpm's but not at higher rpm's, it's probably not the ignition since more demand on the ignition at higher rpm's would make it worse not better. But anything is possible working on engines. just when you say that can't be it, you find out it is. It's possible it could be one of the circuits in the carburetor is partially plugged. It could be at a transfer point in the carb's circuits to where just a little more rpm and it switches circuits, and the problem goes away. You can try raising the rpm to the point it was missing and spray some carb spray into the engine and see if the engine smooths out. That give you an idea if it's a fuel, ignition or engine mechanical problem
You can take a spray can of carb cleaner with the straw attachment and force it into each of the carb's circuits to make sure it blows clean through the plumbing and come out the other end of each passage. I was mechanic during the carb years and every once in a while, you get lucky unplugging a passage in the carburetor that way. We also used to rev the engine and stick our hands on top of the carb while it was at higher rpm, off of the idle circuit. Plugging it with our hands momentarily created a really high vacuum which sometimes unplugged the passage. That might have worked one out of the ten times that we tried it. We were a fleet so if we could fix it without rebuilding the entire carburetor, we did it. 400 vehicles with 400 carburetors there was practically a problem a day with a carburetor, especially if the vehicle was not get driven enough. The carbs dry out and something can go wrong in them
You can do a cylinder defeat test to see if it's one cylinder is causing the problem. Normally you run the engine and pull one plug wire at a time and see how the engine reacts. The rpm should go down a little as each cylinder is removed and then recover as it's plugged back on. It best to go ahead and remove all the wires and just set them back on the plugs to make it easier to unplug them during the test. They should all have the same effect as each one is remove. When you remove a plug wire, and it has no effect on the rpm that's the cylinder with the problem. You "need" a good pair of insulated pliers to grab the spark plug wires with or you will get the crap shocked out of you, you will probably get the crap shocked out of you even good pair of plyers. You are "not" supposed to do that test that way if you have electronic ignition. The voltage is so high it can look for another path to ground by travelling back up though the wire and into the module, burning a microscopic hole in it. It may run another 20,000 miles but that hole will grow until the component fails. You won't realize that you actually caused the problem to happen by just pulling a plug wire off while it was running. If it's an old fashion points ignition, have fun pulling plug wires to find the misfire, you won't hurt a thing except maybe yourself getting zapped.
On the electronic ignitions they make an insulated spark plug tool you hook the wire too, so it still has a place to fire to ground. The problem with that is you need to shut the engine off and switch to the next cylinder and then restart it. You don't have the advantage of hearing the rpm's drop as you are removing the plug wire as it's running. You just have to guess if it's running worse or not with the spark plug wire grounded. The tool does offer the advantage of being able to see the spark on each cylinder.
Spark plug tool for checking for misfires on electronic ignition systems. $15.99
